Project goals for the next fiscal year: (a) To analyze the specificity of mammalian sarcoma type C virus-induced cell surface antigens. (b) To determine the relationship between pristane and Abelson's virus in plasmacytoma-induction. (c) To study the effect of lyophilized Streptococcus hemolyticus on type C virus-replication. (d) To prove the heterogeneity of endogenous type C viruses by the specificity of surface antigens. (e) To identify a new surface antigen (MEV-SA1) induced by a certain endogenous type C virus. (f) To demonstrate the role of blood platelets in the growth of type C virus- induced tumors. (g) To study Ly-4.2 alloantigen distribution on the surface of lymphoid cells as a method for determining B cells. (h) To analyze specific antigenic determinants p15 and gp70 on the type C virus envelope. (i) To detect natural antibody in primates' sera against gibbon and baboon type C viruses. (j) To study the relationship of fetal antigens to tumor-specific antigens using F1 hybrid mice. (k) To locate carcinoembryonic antigen on human malignant cell surfaces. (1) To determine characteristics of a new type C virus isolated originally from transplanted SJL/J spontaneous reticulum cell neoplasm. (m) To examine a difference in tumor regression associated with the appearance of Gross leukemia virus pseudotypes in AKR and C58 mice.